Foam Shell Research Articles

Implosion dynamics of a megampere wire-array Z-pinch with an inner low-density foam shell at the Angara-5-1 facility

The implosion dynamics of a pinch with a highly inhomogeneous initial axial distribution of the load mass was studied experimentally. A cascade array consisting of a double nested tungsten wire array and a coaxial inner cylindrical shell located symmetrically with respect to the high-voltage electrodes was used as a load of the Angara-5-1 high-current generator. The cylindrical foam shell was half as long as the cathode− anode gap, and its diameter was equal to the diameter of the inner wire array. It is shown experimentally that two stages are typical of the implosion dynamics of such a load: the formation of two separate pinches formed as a result of implosion of the wire array near the cathode and anode and the subsequent implosion of the central part of the load containing the cylindrical foam shell. The conditions are determined at which the implosion of the central part of the pinch with the foam cylinder is preceded by intense irradiation of the foam with the soft X-ray (SXR) emission generated by the near-electrode pinches and converting it into the plasma state. Using such a load, which models the main elements of the scheme of a dynamic hohlraum for inertial confinement fusion, it is possible to increase the efficiency of interaction between the outer accelerated plasma sheath and the inner foam shell by preionizing the foam with the SXR emission of the near-electrode pinches.

Cool-down performance of the new apparatus for fuel layering demonstrations of FIREX targets

FIREX targets have been developed under two layering strategies: foam shell and cone guide laser heating methods. Basic studies have been conducted by the collaboration research between ILE and NIFS. Then the next stage requires the characterization of a layered solid fuel. The present system is at the disadvantage of optical observations. Therefore, a new apparatus is designed to solve it. Glass windows with a wide aperture are installed for an interferometer and a microscope. To isolate the vibration from a cryocooler, active vibration control units are equipped, and flexible thermal conductive links are utilized. Furthermore, a quick target exchange mechanism is applied to deal with different types of FIREX targets. A target holder is detachable from a main vacuum chamber. A metal gasket with not fixing bolts but a load of ∼ thousand newtons on ensures GHe leak tightness for target cooling. Eventually, the design temperature of 10.00 K at a target container has been achieved. The cool-down performance indecates that the new apparatus provides a cryogenic environment for fuel layering demonstrations.

Fabrication by photoinitiated polymerization and characterization of millimeter‐size poly(divinyl benzene) hollow foam shells

ABSTRACTIn this study, millimeter‐size compound droplets were prepared easily by a one‐step microfluidic method. We varied the diameter and wall thickness of the shells over a wide range by setting the flow rate. Poly(divinyl benzene) (PDVB) shells with a 3–4.8 mm diameter were fabricated through photopolymerization and supercritical drying. The gel point of photopolymerization was monitored by a rotational rheometer. Moreover, the influence of the oil‐soluble photoinitiator phenyl bis(2,4,6‐trimethyl benzoyl) phosphine oxide (BAPO) on the properties of the foam shell were investigated by transmission electron microscopy, scanning electron microscopy, and nitrogen sorption measurements. Significant differences in the mechanical properties and porous features were obtained for different BAPO concentrations. The surface areas of the foam shells decreased, and the densities of the foam shells increased with increasing BAPO concentration. In addition, the nonconcentricity and out‐of‐roundness values were mainly less than 7 and 3%, respectively, for most of the shells. The results indicate that the PDVB hollow foam shells are a promising inertial fusion energy target. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41625.

FIREX foam cryogenic target development: residual void reduction and estimation with solid hydrogen refractive index measurements

Voidless fuel solidification within a foam material is attempted for the development of a Fast Ignition Realization EXperiment (FIREX) target. A typical target consists of a foam shell with a thin solid fuel layer, a gold cone guide and a glass fill tube. The foam layer is formed with aggregations of tiny cells. The porous foam material has the advantage of forming a uniform layer in a liquid state by the effect of capillarity. Random liquid–solid transitions of fuel, however, would cause void spaces in each cell because of their different densities. To form a voidless solid fuel layer in the FIREX target, we propose a layering method, which includes the process of controlled solidification and simultaneous liquid fuel supply to the liquid/solid interface. Normal H2 is used as a surrogate fuel for our experiments. By applying a resorcinol/formalin aerogel, which has been developed in the Institute of Laser Engineering, Osaka University, instead of a foam material, formation of a solid H2 layer with reduced void spaces is preliminarily demonstrated. Related solid H2 refractive indices are measured to estimate the void fraction. Eventually, its filling factor reaches ∼99%. Furthermore, the application of the proved method is numerically simulated on the FIREX target. The method is confirmed to be applicable in it with a cone guide heating technique.

X射线相衬成像法在线表征冷冻靶技术

A brief review of X-ray phase contrast imaging theory for spherical objects is given. Using Tracepro, simulated X-ray phase-contrast images of SiO2/DD cryogenic capsules are produced. The ability of phase contrast enhanced X-ray imaging for characterization of cryogenic fuel layers inside ablator shells has been proven with the simulation result. X-ray phase contrast imaging equipment has been established for characterization of cryogenic targets, with which imaging experiments for low density divinyl benzene foam shells and SiO2/DD cryogenic capsules have been carried out, and phase contrast images of cryogenic DD fuel layers in SiO2 capsules are obtained, with a resolution up to 1.5 m. Ablator and cryogenic fuel layers can be simultaneously characterized by X-ray phase contrast imaging.

Recent progress of fuel layering study for FIREX cryogenic target

The collaboration research of ILE and NIFS has made progress on the FIREX target developments. We have two fuel layering strategies: a foam shell method and a conical laser guide heating technique. To date, preliminary and principle demonstration stages on both fuel layering methods have been reached. This paper describes the present status of the target developments.

An experimental and numerical study of blast induced shock wave mitigation in sandwich structures

The liners of US military helmets are typically made using common soft foams. In order to better protect troops from Traumatic Brain Injury resulting from Improvised Explosive Devices, it is necessary to better understand the material properties involved in air blast mitigation. In this work, mitigation properties are studied using sandwich samples made from a vinyl-nitrile foam shell filled with materials which were selected to span a range of material properties. These materials—water, glycerin, glass beads, Aerogel®, CAB-O-SIL®, tuff volcanic rock, and expanding foam—were compared to both uniform vinyl-nitrile foam and a US Army helmet pad. Possible modes of shock attenuation include inertial effects based on density and acoustic impedance, dispersion based on porosity, and thermal effects. Since no standard test exists, we developed two experimental configurations to evaluate performance. The results were additionally used to verify a numerical model made using ABAQUS® software. Both the numerical model and the experimental results were consistent in showing that most materials attenuate the peak blast pressure while Aerogel® actually enhances the blast. Density and acoustic impedance mismatch are shown to be of primary importance while porosity is shown to have an effect as well. Furthermore, a differentiation is made between reflective and absorptive shock mitigation.

A new approach to foam-lined indirect-drive NIF ignition targets

Taking full advantage of the unique laboratory environment created by the National Ignition Facility (NIF) will require the availability of foam-lined indirect-drive inertial confinement fusion targets. Here, we report on a new approach that enables fabrication of target structures that consist of a thin-walled (<30 µm) ultra-low-density (<30 mg cm−3) hydrocarbon foam film inside a thick-walled, ∼2 mm diameter ablator shell. In contrast to previous work on direct-drive targets that started with the fabrication of foam shells, we use a prefabricated ablator as a mold to cast the foam liner within the shell. This work summarizes crucial components of this new approach, including the aerogel chemistry, filling of the ablator shell with the aerogel precursor solution with nanolitre precision, creating uniform polymer gel coatings inside the ablator capsule, supercritical drying and doping.

Influence of a density mismatch on TMPTMA shells nonconcentricity

AbstractSome laser target designs require low‐density organic foam shells to study fusion on the French high‐power laser laser mega joule. Low‐density trimethylolpropane trimethacrylate foam shells composed of C, H, and O, 2 mm diameter, 100‐μm wall thickness, and 250 mg cm−3 density are synthesized by a microencapsulation technique using a droplet generator. These shells have to reach a sphericity higher than 99.9% and a nonconcentricity (NC) lower than 1%. The wall thickness variation is one of the most difficult specifications to meet. An important factor in reducing this defect is the density matching between the three phases of the emulsion at polymerization temperature. The influence of a density mismatch between the internal water phase and the organic phase on the NC of TMPTMA foam shells was studied. The best NC results and yields of shells are obtained with a density gap between the internal water phase and the organic phase of 0.078 g cm−3 at 60°C, with an average NC around 2%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Study on the surface roughness of ceramic shells and castings in the ceramic shell casting process based on expandable pattern

A method to form a thin smooth film of wax on the surface of the foam pattern was proposed by introducing the molten wax in this work. Organic smoothing coatings for the foam pattern were also prepared and their effects on the surface roughness of the foam patterns, shells and castings were investigated. Effects of the facecoat slurry used to fabricate ceramic shells on the surface roughness of the shells and castings were studied. The analysis of results indicates that the surface smoothing coatings and the wax smoothing film both greatly decreased the surface roughness of ceramic shells and castings from 3.2–6.3 μm to 0.8–2.5 μm (Ra), and the surface roughness of shells and castings would be improved if the facecoat slurry is prepared with finer filler materials.

Development and Fabrication of NIF-Scale Resorcinol Formaldehyde Foam Shells for ICF Experiments

Possible designs for future direct- and indirect-drive targets required for the National Ignition Facility (NIF) include resorcinol formaldehyde (R/F) foam shells. Depending on the experiment type, the shell dimensional specifications can range from 1.5- to 3.5-mm diameter with a 100- to 200-μm wall. This paper will discuss the adjustments and modifications of the process developed for smaller-diameter (˜900-μm) OMEGA-scale R/F shells that were used to fabricate these higher-aspect-ratio NIF-scale shells.

Impact of the Foamed Aluminum-Filled Structures

The carrying capacity and energy absorption characteristic of foamed aluminum (or aluminum foam), fabricated by melt foaming technique, are limited due to the lower strength of aluminum. The typical anti-vibration energy absorbing structures are designed as foamed aluminum-filled or sandwich structures. The deformation and absorption characteristics of foamed aluminum-filled structures subjected to impact loadings are analyzed using experimental and numerical methods in this work. The analysis shows that the steel shell of the combinative structure subjected to dynamic loadings dominates during energy absorption. The energy absorption capacity and initial instability loading increase as impact velocity increase and as increasing shell thickness duo to the interaction between steel shell and aluminum foam. The impact mass within the range of 100kg influences weakly on peak instability loading. Since the steel shell is the dominating part of load capacity and energy absorption, the reasonable design, taking into account of foam density and shell thickness and taking full advantage of interaction between steel shell and aluminum foam, should be adopted to increase the energy absorption characteristic of foam-filled structures.

Target developments program to prepare LMJ campaigns

To carry out laser plasma experiments on CEA laser facilities, a R&D program was set up and is still under way to deliver complex targets. For a decade, specific developments are also dedicated to "Ligne d'Intégration Laser" (LIL) in France and Omega facilities (USA). To prepare the targets intended for the first experiments on the Laser "Mégajoule" (LMJ) facility, new developments are required, such as cocktail hohlraum fabrication, gas barrier coating and foam shells developments. For fusion experiments on LMJ, an important program is also under way to elaborate the Cryogenic Target Assembly (CTA), to fill and transport the CTA and to study the conformation process of the DT layer.

The effect of the Rim Cutter™ on cement pressurization and penetration on cemented acetabular fixation in total hip arthroplasty: An in vitro study

The Rim Cutter (Stryker Orthopedics, Mahwah, New Jersey) is a tool designed to cut a ledge inside the rim of the acetabulum, onto which a precisely trimmed, cemented, flanged cup can be fitted. The aim was to investigate the effect of the Rim Cutter on the intra-acetabular cement mantle pressure and the depth of cement penetration during cup insertion. The study had two parts. In the first part, hemi-pelvis models were fitted with pressure sensors. Pressure in the acetabulum was measured on insertion of a conventional cemented flanged cup with and without the use of a Rim Cutter to prepare the rim of the acetabulum. The second part assessed cement penetration when the same cups were inserted into a foam shell model. The shell was mounted in a jig and had holes drilled in it; the distance that cement penetrated into the holes was measured. A significant increase in cement pressure at the apex (p = 0.04) and the rim (p = 0.004) is seen when the Rim Cutter is used. Cement penetration in the Rim Cutter group was significantly increased at the rim of the acetabulum (p = 0.003). Insertion of a flanged cup after the acetabulum is prepared with the Rim Cutter leads to a significant increase in cement pressure and penetration during cup insertion in vitro when compared with conventional flanged cups.

二乙烯基苯泡沫空心球微流体成型技术

二乙烯基苯泡沫空心球微流体成型技术

Temperature Control in a Cryogenic Target with a Conical Laser Guide for Fuel Layering

Fuel layering of a cryogenic target with a conical laser guide such as the FIREX target is complicated because of its non-spherical symmetry appearance. To simplify the layering, a foam layer is planned to utilize as a supporting material of fuel. Ideally, the foam shell has self-fuel-layering ability at a liquid state owing to the capillarity of the foam material. For stable fuel compression in laser experiments, the fuel must be solid with a lower saturated pressure. The transition to a solid state expects to cause random fuel crystallization and voids from the density difference between liquid and solid. A volumetric heat load might help to finish fuel layering even in the foam shell. Solid fuel redistribution will ignore the foam boundary. Temperature control in the target, therefore, is required during the formation of a uniform layer. For the rough estimation of the target temperature, the possibility of the ANSYS code was confirmed compared with the experiment using a dummy target. Then, steady state temperature profiles of the FIREX target were calculated using the ANSYS code. Temperature control to practically realize a uniform solid fuel layer in the FIREX target is discussed.

Impact dynamics of metal foam shells for motorcycle helmets: Experiments & numerical modeling

To reduce the weight of motorcycle helmet, metal foam for outer shell in place of conventional thermoplastics was tested. The dynamic behaviour of this new helmet was studied through experiments and numerical modeling. Open-face motorcycle helmets were designed with metal foam shell and impact experiments were performed with these helmets fitted on a headform. A finite element model was developed and the predicted acceleration of headform from this model was validated against the experiments. The mechanical behaviour of full-face helmets with metal foam shell was investigated next. The FE analysis was performed separately with rigid and deformable heads. Head injury criterion (with rigid head) and stresses in brain (with deformable head) were evaluated separately for metal foam shell and ABS shell helmets. The helmet impact performance is examined with two separate densities of metal foam. The shell with low-density metal foam (150 kg/m 3) gives a better performance compared to ABS shell. The metal foam shell showed significant visible plastic deformation in the impact region.

Improvements on Permeation GDP Coatings for Resorcinol Formaldehyde Foam Shells for Cryogenic Experiments on OMEGA

Resorcinol formaldehyde (RF) foam shells are needed for direct-drive inertial confinement laser fusion experiments at the University of Rochester OMEGA laser facility. As previously reported, the addition of long-chained polymers to the fabrication process has improved shell wall uniformity, but this change has led to a lower yield (from ~40 to ~15%) of shells that are gas retentive after the application of glow discharge polymer (GDP) using the standard deposition technique. We have improved this yield by modifying the coating conditions of the GDP overcoating process by modifying the background coating pressure from the constant 75 mTorr to using a two-step coating process of a high-pressure coating at 250 mTorr followed by low-pressure coating of 75 mTorr. This modification has improved the yield of the gas retention on the styrene-butadiene-styrene RF shells from ~15 to ~60%. We have found that the surface roughness of these shells is also improved from ~45 nm root-mean-square (rms) to ~20 nm rms. This technique, however, leads to a slight shrinkage of shells, which will be described.

Three-Dimensional Wallmapping Using Xradia with Distortion Correction

The inertial confinement fusion program requires the uniformity of multilayered samples to be measured to high accuracy. We currently use a reflection spectroscopy tool to measure optically transparent shells with no more than two layers. The method cannot measure opaque samples such as beryllium shells, low-reflection samples such as foam shells, or any shells with more than two layers such as National Ignition Facility specification Ge-CH shells. We also use a white-light interferometer to measure transparent samples with multiple layers, but only at the North/South Poles for a given orientation. To complement these existing tools, we developed an X-ray technique based on a commercial X-ray microscope (Xradia MicroXCT). MicroXCT is capable of providing high-contrast, high-resolution images and allows the samples to be precision aligned and angular indexed. Dimension accuracy is achieved through the calibration of the projection magnification and the lens distortion. From each X-ray image, a wall thickness trace along the great circle is obtained by converting Cartesian coordinates into cylindrical coordinates, and edge-finding algorithms are developed for a contact radiography project. Three-dimensional reconstruction and wall thickness display allow the visualization of the sample nonuniformity. The method has a 0.3 μm measurement precision and, through phase contrast calibration, can achieve 0.3 μm accuracy.

Advancements in Glow Discharge Polymer Coatings for Mass Production

The horizontal rotary glow discharge polymer (GDP) coater is being developed to help increase the production rate of inertial confinement fusion targets and to meet the very high production rates needed for inertial fusion energy targets. The coater is used to put a conformal GDP gas retention coating on top of foam shell targets. A number of alterations to the design and operation of the horizontal rotary GDP coater are discussed. Compared to previous iterations of the horizontal coater, the changes have resulted in improving the yield of gas retentive targets with thinner coatings and increasing the coating rate, smoothness, and uniformity. The number of targets that can be coated at once has increased from tens to hundreds, or even thousands. The alterations include changing the coating tube configuration; adjusting the coating pressures; and altering the radio-frequency power, gas flow rates, and tube rotation rates. Methods to further improve the coater are also discussed.